In order to extend digital service to customer premises equipment (CPE) served by a remote terminal (RT), telephone networks customarily employ a digital loop carrier (DLC) system, such as T1 carrier system for time division multiplexed data format (e.g., Bellcore standard TR-NWT-000397) diagrammatically illustrated in FIG. 1. In this ‘universal’ type of DLC system, opposite ends of the digital carrier communication link (the T1 link) 10 are coupled to a central office terminal (COT) 12 and a remote terminal (RT) 14, respectively. For multiplexing and demultiplexing digital traffic conveyed over the T1 carrier link 10 with digital subscriber loops (DSL)s 21 of an associated switch 20 (such as an AT&T 5ESS switch), the central office terminal 12 may contain a plurality of digital loop carrier circuits 13, such as basic rate interface transmission extender cards, commonly referred to as BRITE cards or U-BRITE cards. Each BRITE card 13 is coupled over a respective DSL 21 to one of a plurality of line cards 23 of the switch 20. In a complementary manner, the remote terminal 14 may contain a plurality of BRITE cards 15, respectively associated with DSLs 16 serving respective CPEs.
For digital switch applications, the digital subscriber loops 21 between the switch 20 and the COT 12 become superfluous and may therefore be eliminated by terminating the carrier link to the remote terminal with the switch. For this purpose, two Bellcore ‘integrated’ digital loop carrier systems—TR-NTW-0008 and GR-CORE-303—have been proposed. The purpose of these systems is to reduce the cost per subscriber (by eliminating the subscriber loops between the switch and the COT), and to increase bandwidth efficiency by concentration at the carrier facilities.
However, each has its shortcomings. First of all, the TR-NTW-0008 system does not provide for deployment of ISDN signalling. Secondly, the GR-CORE-303 system, which does deploy ISDN, involves a substantial modification of the configuration of the switch, requiring a substantial capital investment, that is passed on to the subscriber in the form of higher costs (which become prohibitive in areas of low subscriber density).